Helical Steel Stairs
Helical Steel Stairs
(OP)
I know this issue has come up before, and I've read the old posts, but I have not seen a definitive answer on how to design helical steel stair stringers. I found reference to an out-of-print book "Staircase: Structural Analysis and Design" by M.Y.H. Bangash that sells for $166-$255, but I really don't want to spend that kind of money, and I don't know if it addresses steel members. Bangash's book refers to Morgan's Method and Cohen's Method, but I'm unable to find any literature for either of those references, and I'm not even sure they relate to steel stairs either.
An eng-tips post from 2000 refers to "Design Charts for helical stairs with fixed supports by A.R. Cusens & S. Santathadaporn", but I can't find that literature either.
I know there are big time torsional issues as well as thrust at the bottom of the stairs. Does anybody have a clue as where to start?
An eng-tips post from 2000 refers to "Design Charts for helical stairs with fixed supports by A.R. Cusens & S. Santathadaporn", but I can't find that literature either.
I know there are big time torsional issues as well as thrust at the bottom of the stairs. Does anybody have a clue as where to start?






RE: Helical Steel Stairs
RE: Helical Steel Stairs
Following from Google:
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RE: Helical Steel Stairs
racookpe... if only it had a center post and was that simple. This is a monumental "Gone With The Wind"-type stair.
RE: Helical Steel Stairs
http://www.snopes.com/horrors/ghosts/loretto.asp
RE: Helical Steel Stairs
I've built a couple like that for high-end homes, but not for commercial. But in most, the swept, spiral curving wood steps and framing were already in place, and all I needed to do was design and style and bend and weld the wrought iron, design and bend the handrails and brackets, weld up and grind smooth everything, and fab the whole thing in place in the housewife's living room ...
Treat it like two springs being compressed: the outer spring steel is the outside frame, the inner spring (different radius and spiral) is the second. Don't get too fancy with the steps - they are a simple beam held at both ends. You want each "spring" to hold half your total steps load (nbr of steps x expected load per step / 2) without compressing too much - both should ideally compress the same actually. From compressed spring theory, then you "translate" the spring section modulus to a equivalent beam.
Then you roll and twist the two beams so they are equal distances apart. It is easier to roll and twist tube steel or solid bars, NOT I-beams/angles or channels or w shapes. The absolute easiest - because you HAVE to "twist" the beam sections as you turn them into a spiral is a solid round. The round bar is more forgiving as you twist it, because your eye won't see small changes and distortions. A flat bar must be twisted "perfectly" to look right.
RE: Helical Steel Stairs
RE: Helical Steel Stairs
RE: Helical Steel Stairs
RE: Helical Steel Stairs
Sideways forces that are developed (created) are from the max distance (lever arm) between the points of attachment at the top (and the bottom) and the load as it walks down the spiral. This lever arm will act to "pull" the stair away from the upper platform
shear force at the bottom is small: think of a the sheer force caused by a screw thread: the sideways force from a screw thread is the product of the slope of the screw thread.